CRYSTALS AND ORGANISMS 3 



have life is growth: crystals also grow, but not in the same 

 way. The method of growth in crystals is by accretion, i. e., 

 by addition of substance to the outside; but in the growth of 

 living organisms the added substance is taken up into the 

 interior of the body, i. e., by intussusception. Moreover, in 

 crystals the chemical nature of the substance added is not 

 altered, while in the case of organisms the substance added 

 undergoes a series of chemical changes before it is finally 

 really part of the growing body. This process of transforming 

 food material is called assimilation and is wholly wanting in 

 crystals. 



7. Another prominent characteristic of organisms is the 

 definiteness of the shapes which they assume. Each plant or 

 animal is as much like every other individual of the same 

 kind as if they were all made after the same pattern or cast 

 in the same mold. Crystals are bounded by plane surfaces 

 which meet at definite angles but within this limitation the 

 shape may vary indefinitely. 



8. The size of organisms is limited. The individual grows 

 more or less rapidly until it reaches a certain size after which 

 growth almost or wholly ceases. The size of crystals has no 

 definite limitations. 



9. Crystals may be formed under favorable circumstances 

 wherever the substances of which they are composed are found. 

 But we have no knowledge that a living thing is ever formed 

 under any conditions except by development from what we 

 may call a germ, which came from some pre-existing living 

 thing, and which differs from the mature organism chiefly in 

 being smaller and simpler in structure. The crystal may be 

 reduced to its constituent elements which will again unite 

 under the proper conditions to form a new crystal, whereas if the 

 organism is similarly reduced, its elements will under no condi- 

 tions recombine to produce a new organism. 



10. Crystals may exist indefinitely, but the life of the in- 



